Variable speed gearing system

ABSTRACT

A variable speed gearing system includes two clutch units  30, 50  placed side by side in the axial direction and provides a plurality of transmission gear ratios in response to the state of engagement of clutches  31, 51  of the two clutch units  30, 50 . Axially movable members  26   a   , 48   a  of the two clutch units  30, 50  are arranged in such a manner as to confront each other. A damper mechanism  60  is constituted by the combination of a piston member  62  provided on one of the confronting axially movable members  26   a   , 48   a  and a cylinder member  61  provided on the other thereof.

TECHNICAL FIELD

The present invention relates generally to a variable speed gearingsystem and, more particularly, to a mechanism for suppressing orreducing shocks (gear shift shocks) or vibrations/jars (gear shiftjudders) which may occur upon gear shifts.

BACKGROUND ART

Variable speed gearings designed to change the transmission gear ratiosby engagement/disengagement of clutches have hitherto been known.Japanese Patent Laid-open Pub. No. Hei 6-505082 discloses by way ofexample a variable speed gearing of the type in which the clutches areengaged or disengaged by thrust forces applied to centrifugal clutchesand planetary gears.

In the case of such clutches, the clutch engagement and disengagementare mechanically carried out, making it difficult to regulate andcontrol the motions of the clutches, which often resulted in occurrenceof gear shift shocks or judders upon gear shifting.

In the event of variable speed gearings which effect the gear shifts bythe hydraulic drive of the clutches, a smooth clutchengagement/disengagement can be achieved by finely controlling thehydraulic pressure, although hydraulic pressure control means arenecessitated resulting in a complicated structure.

DISCLOSURE OF INVENTION

It is an object of the present invention to provide a variable speedgearing system having a simple structure to reduce any shocks or judderswhich may be induced by gear shifts.

According to an aspect of the present invention, in order to attain theabove object, there is provided a variable speed gearing systemincluding two clutch units placed side by side in the axial direction,the variable speed gearing system providing a plurality of transmissiongear ratios in response to the state of engagement of clutches of thetwo clutch units, the two clutch units being provided with axiallymovable members confronting each other; the variable speed gearingsystem comprising a piston member provided on one of the axially movablemembers confronting each other; and a cylinder member provided on theother of the axially movable members confronting each other, the pistonmember and the cylinder member constituting a damper mechanism incombination with each other.

Since the damper mechanism provides a resistance against the axialmovements of the movable members upon the gear shifts depending on therate of movements, it is possible to suppress any abrupt movement toensure a smooth engagement and disengagement, to thereby reduce anypossible gear shift shocks or gear shift judders.

Furthermore, the damper mechanism is constituted by the combination ofthe piston member and the cylinder member with utilization of the spacedefined between the two axially movable members confronting each other,whereby it is possible for the variable speed gearing system to have asimple configuration and reduced dimensions without any need to provideeach clutch with a dedicated damper mechanism and without any need for adedicated space therefor.

The variable speed gearing system may further comprise an oil chamberdefined by the piston member and the cylinder member in cooperation, theoil chamber having an expanded or contracted volume; and communicationpassages extending from oil passages formed within shafts for axiallymovably supporting the movable members of the clutch units, into the oilchamber.

Thus, the oil chamber can be at all times fed with oil from the oilpassage within the shaft through the communication passages, and the oildamper mechanism is implemented by the orifice effect of thecommunication passages allowing the oil to flow in and out due to theexpansion and contraction of the oil chamber, whereby it is possible toachieve a smooth clutch engagement/disengagement to reduce the gearshift shocks or the gear shift judders.

The variable speed gearing system may further comprise flow controlmeans disposed in the communication passages for imparting differentpassage areas to the communication passages between expansion andcontraction of the oil chamber.

The relationships between the gear shift patterns and the magnitudes ofthe gear shift shocks will differ depending on the circumstances of useof the variable speed gearing system.

Thus, the flow control means provide a control so as to ensure that thepassage areas of the communication passages become smaller upon theexpansion if the gear shift patterns expected to present greater gearshift shocks occur upon the expansion of the oil chamber but that thepassage areas become smaller upon the contraction if the gear shiftpatterns expected to present greater gear shift shocks occur upon thecontraction of the oil chamber, whereby their resistances are increasedso that the gear shift shocks can effectively be suppressed.

BRIEF DESCRIPTION OF DRAWINGS

FIG. 1 is a schematic diagram of the configuration of a variable speedgearing system in accordance with an embodiment of the presentinvention;

FIG. 2 is a sectional view showing a specific structure of an oil damperin the first-speed state of the variable speed gearing system;

FIG. 3 is a sectional view showing a specific structure of the oildamper in the second-speed state of the variable speed gearing system;

FIG. 4 is a sectional view showing a specific structure of the oildamper in the third-speed state of the variable speed gearing system;

FIG. 5 is a sectional view showing a specific structure of the oildamper in the third-speed state of the variable speed gearing system;

FIG. 6 is a sectional view of the oil damper having flow control meansdisposed in a communication passage leading into an oil chamber of theoil damper;

FIG. 7 is a sectional view of the oil damper having different flowcontrol means disposed in the communication passage leading into the oilchamber of the oil damper;

FIG. 8 is a sectional view of the oil damper provided with a one-wayvalve;

FIG. 9 is a sectional view of the oil damper provided with anotherone-way valve; and

FIG. 10 is a sectional view of the oil damper provided with a furtherone-way valve.

BEST MODE FOR CARRYING OUT THE INVENTION

The present invention will now be described with reference to FIGS. 1 to5 which illustrate a preferred embodiment thereof. FIG. 1 depicts aschematic configuration of a variable speed gearing system 1 inaccordance with the embodiment.

The variable speed gearing system 1 is capable of varying the speed infour steps from the first speed to the fourth speed in addition toneutral and provides a combination of front two steps and rear two stepsallowing four-step gear shifts.

A front centrifugal clutch 30 shifts the front two steps and a rearcentrifugal clutch 50 shifts the rear two steps. An electromagneticbrake 10 is provided for neutral.

A gear shift mechanism comprises a base shaft in the form of an inputshaft 2 which directly receives a rotational driving force from theengine. The electromagnetic brake 10 comprises a fixed annular outermember 11, an exciting coil 12 arranged on the inner periphery of theouter member 11, and an inner member 13 rotatably supported on theinside of the coil 12. The inner member 13 is coupled by means ofsplines for example to a cylindrical rotary member 14 which is rotatablysupported on the input shaft 2.

At one end of the cylindrical rotary member 14 coupled to the innermember 13 in this manner, a sun gear 21 is provided via a one way clutch15 so as to rotate jointly, the sun gear 21 constituting a fronttwo-step planetary gear mechanism.

In addition to the sun gear 21, the front planetary gear mechanismincludes a planetary gear 22 which mates with the sun gear 21 andrevolves around the sun gear 21 with rotations around its own rotationalaxis, and a ring gear 23 meshed externally with the planetary gear 22.

The ring gear 23 is coupled via a ring member 24 to the input shaft 2,with the planetary gear 22 being coupled via a carrier 25 to the rearstep.

The carrier 25 itself rotates carrying the planetary gear 22 but isprohibited from its axial movement, although it is provided with anouter tubular portion in the form of a clutch guide 26 which is splinefitted around the carrier 25 in such a manner as to be slidable in theaxial direction.

The sun gear 21, the planetary gear 22 and the ring gear 23 are helicalgears each having teeth twisted oblique to the gear axis. When a hightorque is applied from the input shaft 2 to the ring gear 23, the latteris subjected to an axially urging force, which in turn acts in adirection allowing the clutch guide 26 to move together via a thrustbearing 68 (see FIG. 2) to thereby disengage a multiple disc clutch 31.

The centrifugal clutch 30 is interposed between the clutch guide 26 andthe ring member 24. The centrifugal clutch 30 is provided in the form ofthe multiple disk clutch 31 which includes a plurality of discsextending perpendicular to its axis in the portion where the clutchguide 26 and the ring member 24 form an outer tube and an inner tube,respectively, with the plurality of discs alternating with one anotherso as to permit an appropriate axial sliding movement. A centrifugalweight 32 serves to cause an axial relative movement of the clutch guide26 relative to the ring member 24, to thereby effect the engagement anddisengagement of the multiple disc clutch 31.

Rotation of the carrier 25 gives rise to a movement of the centrifugalweight 32 in the centrifugal direction, this movement being accompaniedby a sliding movement of the clutch guide 26 in the axial direction(leftward in FIG. 1), whereupon once a predetermined number of times isexceeded, the clutch guide 26 relatively moves relative to the ringmember 24, allowing the engagement of the multiple disc clutch 31.

On the other hand, the rear two-step gear shifts are also achieved by aplanetary gear mechanism and a centrifugal clutch 50. A sun gear 41 isspline coupled to a cylindrical rotary member 40 in such a manner as tobe rotatable jointly, with the cylindrical rotary member 40 being splinefitted to the clutch guide 26 of the carrier 25.

In addition to the sun gear 41, the rear planetary gear mechanismincludes a planetary gear 42 which mates with the sun gear 41 andrevolves around the sun gear 41 with rotations around its own rotationalaxis, and a ring gear 43 meshed externally with the planetary gear 42.

A ring member 44 provided with the ring gear 43 is engagedunidirectionally with a fixing portion 46 by way of a one way clutch 45.

A carrier 47 for rotatably supporting the planetary gear 42 is splinecoupled to an output shaft 3 which is provided with an output gear 4.

The carrier 47 is provided with an outer tubular portion in the form ofa clutch guide 48 which is spline fitted around the carrier 47 in such amanner as to be slidable in the axial direction.

The sun gear 41, the planetary gear 42 and the ring gear 43 constitutingthe planetary gear mechanism are helical gears each having teeth twistedoblique to the gear axis. When a high torque is exerted on the sun gear41 coupled to the cylindrical rotary member 40 which is spline fitted tothe front output shaft (clutch guide 26), the sun gear 41 is subjectedto an axially urging force, which in turn acts in a direction allowingthe clutch guide 48 to move together to thereby disengage a multipledisc clutch 51.

The centrifugal clutch 50 is interposed between the clutch guide 48 andcylindrical rotary member 40.

The centrifugal clutch 50 Is provided in the form of the multiple diskclutch 51 which includes a plurality of discs extending perpendicular toits axis In the portion where the clutch guide 48 and the cylindricalrotary member 40 form an outer tube and an inner tube, respectively,with the plurality of discs alternating with one another so as to permitan appropriate axial sliding movement. A centrifugal weight 52 serves tocause an axial relative movement of the clutch guide 48 relative to thecylindrical rotary member 40, to thereby effect the engagement anddisengagement of the multiple disc clutch 51.

Rotation of the carrier 47 gives rise to a movement of the centrifugalweight 52 in the centrifugal direction, this movement being accompaniedby a sliding movement of the clutch guide 48 In the axial direction(rightward In FIG. 1), whereupon once a predetermined number of times isexceeded, the clutch guide 48 relatively moves relative to thecylindrical rotary member 40, allowing the engagement of the multipledisc clutch 51.

Vertical annular walls 26 a and 48 a confront each other with a spacedefined therebetween for accommodating an oil damper 60, the verticalannular wall 26 a on one hand being perpendicular to the axis of theclutch guide 26 acting as an axially movable member for the frontcentrifugal clutch 30, and the vertical annular wall 48 a on the otherbeing perpendicular to the axis of the clutch guide 48 acting as anaxially movable member for the rear centrifugal clutch 50.

From the vertical annular wall 26 a there extends an annular cylinder 61having a U-shaped section and an opening directed toward the verticalannular wall 48 a on the other. From the vertical annular wall 48 athere extends an annular piston 62 similarly having a U-shaped sectionand an opening directed toward the vertical annular wall 26 a on onehand. The piston 62 fits into the interior of the cylinder 61 in afreely slidable and relatively rotatable manner so as to provide the oildamper 60 having an oil chamber 63 formed therewith in.

Description will then be made of the oil damper 60 and its peripheralstructure with reference to FIGS. 2 to 5 which illustrate the same in aspecific manner.

The cylinder 61 associated with the front clutch guide 26 comprises aninner tubular member 61 a fitted to the inner peripheral edge of thevertical annular wall 26 a, and an outer tubular member 61 b fixed tothe annular wall 26 a around the member 61 a, the inner and outertubular members forming a U-shaped section in cooperation. The piston 62associated with the rear clutch guide 48 comprises an inner tubularportion 62 a and an outer tubular portion 62 b which are in advanceassembled into an annular form with a U-shaped section, the assemblybeing fixedly secured to the vertical annular wall 48 a.

The inner tubular portion 62 a and the outer tubular portion 62 b of thepiston 62 are in sliding contact internally with the inner tubularmember 61 a and the outer tubular member 61 b of the cylinder 61,respectively, the sliding contact portions being provided with sealmembers 65 and 66.

A communication hole 64 is formed in the inside corner of the piston 62.

The cylindrical rotary member 40 is slidably inserted between the inputshaft 2 and the inner tubular member 61 a of the cylinder 61, thecylindrical rotary member 40 being spline fitted to the inner tubularmember 61 a.

The cylindrical rotary member 40 is formed with a communication passage40 a extending from its interior up to its exterior. The communicationpassage 40 a communicates with a space defined among the cylindricalrotary member 40, the vertical annular wall 48 a, the inner tubularmember 61 a and the piston 62, and further with the communication hole64.

The input shaft 2 includes therein an oil supply passage 2 a extendingalong its central axis, into which oil is pumped by means of an oil pumpdisposed at its end, the oil supply passage 2 a serving to supply oil toa plurality of desired parts of the variable speed gearing system 1. Theinput shaft 2 further includes a branch passage 2 b extending toward thecommunication passage 40 a of the cylindrical tubular member 40, and acircumferentially extending groove 2 c formed, with a predeterminedwidth, around the outlet portion of the branch passage 2 b so as toallow a communication with the communication passage 40 a at all times.

Oil within the oil supply passage 2 a of the input shaft 2 is suppliedthrough the branch passage 2 b, the groove 2 c, the communicationpassage 40 a, the space 67 and the communication hole 64 into the oilchamber 63 so that the oil chamber 63 is constantly filled with the oil.

The slide bearing 68 is interposed between the vertical annular wall 26a and the ring member 24 in order to ensure smooth relative rotationsbetween the two while freely varying the axial distance therebetweenwithin a predetermined range.

A similar slide bearing 69 intervenes between the vertical annular wall48 a and the cylindrical rotary member 40.

The inventive variable speed gearing system 1 is a four-step speedvariator equipped with the oil damper 60 and using the centrifugalclutches 30 and 50 as set forth hereinabove.

During the neutral, the electromagnetic brake 10 is in its releasedcondition and the centrifugal clutches 30 and 50 are also in theirrespective disengaged conditions.

In this case, rotations of the engine are transmitted to the ring gear23, but are not transmitted to the clutch guide 26 and thence to theoutput shaft 3 since the sun gear 21 is free with the centrifugal clutch30 being released.

When the centrifugal clutches 30 and 50 are in their let-out conditionswith a low engine speed, engagement of the electromagnetic brake 10results in the first speed state.

More specifically, with the sun gear 21 fixed, rotations of the ringgear 23 cause the planetary gear 22 to revolve around the sun gear 21,allowing the carrier 25 to rotate. Rotations of the carrier 25 (clutchguide 26) give rise to rotations of the sun gear 41, which in turncauses the output shaft 3 to rotate at the first speed under the ringgear 43 whose rotations are blocked by the one way clutch 45.

During this first speed, the oil chamber 63 of the oil damper 60 is putin its most compressed state as shown in FIG. 2.

Excepting the neutral, the electromagnetic brake 10 is in its engagedcondition to fix the sun gear 21.

When the front centrifugal clutch 30 is activated in the first speedstate, the clutch guide 26 initially moves leftward in FIG. 1 togetherwith the ring member 24, allowing the oil chamber 63 of the oil damper60 to expand. Once the ring member 24 is halted by the stopper, theresultant relative approach of the clutch guide 26 allows the engagementof the multiple disc clutch 31, whereupon rotations of the input shaft 2are transmitted via the ring member 24 intactly to the clutch guide 26,achieving the second speed state.

In the second speed state, the oil chamber 63 of the oil damper 60 isallowed to have a volume of the extent shown in FIG. 3.

Then, when the increased vehicle speed makes the rear centrifugal clutch50 active, the clutch guide 48 moves rightward in FIG. 1 to allow theengagement of the multiple disc clutch 51. In consequence, rotations ofthe clutch guide 26 in direct connection with the engine are decreasedwith a reduction of the engine speed, whereupon the front centrifugalclutch 30 is let out, achieving the shift-up to the third speed state.

When the ring gear 23 is rotated with the centrifugal clutch 30released, the planetary gear 22 revolves jointly with rotations of theclutch guide 26, with the result that due to the engagement of the rearcentrifugal clutch 50, the rotations of the clutch guide 26 are outputas rotations of the output shaft 3.

The instant that the oil chamber 63 of the oil damper 60 is slightlyexpanded as a result of the rightward movement of the clutch guide 48,engagement of the rear centrifugal clutch 50 and release of the frontcentrifugal clutch 30 take place, whereupon the oil chamber 63 isdisplaced toward the right in its entirety without substantiallychanging its volume.

Then a further increased vehicle speed gives rise to an increase in thenumber of rotations of the front clutch guide 26 which rotates togetherwith the output shaft 3, rendering the front centrifugal clutch 30active, so that the clutch guide 26 is moved toward the left to expandthe volume of the oil chamber 63. When a predetermine number ofrotations is exceeded, the multiple disc clutch 31 is let in, achievingthe shift-up to the fourth speed state.

The engagements of both the front and rear centrifugal clutches 30 and50 allows rotations of the input shaft 2 to be output intactly asrotations of the output shaft 3.

In the fourth speed state, the oil chamber 63 of the oil damper 60 isexpanded to the maximum as shown in FIG. 5.

Upon the kickdown, the helical gears of the front ring gear 23 and therear sun gear 41 generate thrust forces which act in the directionsreleasing the centrifugal clutches 30 and 50, respectively, to reducethe transmission gear ratio.

In particular, upon the kickdown from the fourth speed to the firstspeed, the oil chamber 63 of the oil damper 60 varies greatly from itsmost expanded spate to its most contracted state.

In the event that the accelerator is released after a rapidacceleration, the thrust forces of the helical gears act in thedirection allowing engagements of the clutches 30 and 50, opposite tothe above directions, due to a torque arising from the wheel rotations,i.e., from the vehicle speed. Simultaneously the clutches 30 and 50 aremore securely engaged due to the centrifugal forces, achieving the gearshift. In particular, upon the shift-up from the first speed to thefourth speed, the oil chamber 63 of the oil damper 60 varies to a largeextent from its most contracted state to its most expanded state.

As described hereinabove, upon the shift-up the volume of the oilchamber 63 expands and oil is supplied through the communication hole 64so that the oil damper 60 acts toward the compressive side with aresistance in proportion to the rate of expansion, thereby ensuringrespective smooth engagements of the multiple disc clutches 31 and 51 toreduce any possible shocks induced by gear shifts.

When shifting up from the first speed to the fourth speed in particular,the oil damper 60 acts toward the compressive side under a large amountof variation in strokes, whereby it is possible to achieve respectivesmooth engagements of the front and rear multiple disc clutches 31 and51 to effectively reduce the gear shift induced shocks.

Although the volume of the oil chamber 63 is subjected to substantiallyno change upon the gear shifting from the second speed to the thirdspeed, the chamber 63 serves as a hydraulic piston restricting motionsof the front and rear multiple disc clutches 31 and 51 together, therebyensuring smooth clutch shifting actions and preventing any occurrence ofgear shift judders as well as achieving reduced gear shift shocks.

Also, upon the shift-down, the oil damper 60 acts toward the expansileside so as to ensure that the multiple disc clutches 31 and 51 aresmoothly disengaged to reduce any shocks or judders caused by gearshifts.

Upon the gear shift from the third speed to the second speed, smoothclutch shifting actions are achieved so that the gear shift judders areprevented from occurring with reduced gear shift shocks.

By virtue of the oil damper 60 constituted of the piston 62 and thecylinder 61 in cooperation and utilizing the space defined between thevertical annular walls 26 a and 48 a, which are axially movable membersconfronting each other, of the front and rear centrifugal clutches 30and 50, respectively, it is possible to realize a simple structurewithout any need to individually provide the damper mechanisms on thecentrifugal clutches 30 and 50 as well as to make the variable speedgearing system compact without needing any dedicated spaces.

Referring then to FIGS. 6 and 7 there are illustrated and described twofurther embodiments, respectively, in which the communication hole 64 ofthe oil damper 60 is provided with flow control means.

It is to be noted that the two embodiments have structurallysubstantially the same variable speed gearing systems and oil dampersand that the same members are designated by the same reference numerals.

An oil damper 70 shown in FIG. 6 comprises a substantially L-shapedresilient plate 71 bent on the piston 62 toward the oil chamber 63, theplate 71 having one portion fixedly secured thereto and the otherportion directed to the communication hole 64.

Upon the shift-up giving rise to an expansion of the oil chamber 63 toallow oil to be fed thereinto, the same level of resistance as in theabove embodiment is presented with the resilient plate 71 leaving thecommunication hole 64 open as shown in FIG. 6, whereas upon theshift-down causing a contraction of the oil chamber 63, the resilientplate 71 deforms in the direction closing the communication hole 64,resulting in an increased resistance against oil when it flows out ofthe oil chamber 63 through the communication hole 64.

This means that in cases where upon the shift-down a greater gear shiftshock or judder is expected than in the shift-up, use of the inventiveoil damper 70 ensures an effective reduction in shocks or juddersinduced by gear shifts.

An oil damper 80 shown in FIG. 7 comprises a resilient plate 81protrusively provided in the space 67 outside the oil chamber 63 in sucha manner as to confront the communication hole 64.

Upon the shift-up giving rise to an expansion of the oil chamber 63 toallow oil to be fed thereinto, the resilient plate 81 blocks thecommunication hole 64 as shown in FIG. 7 to provide a great resistanceagainst the flow of oil, whereas upon the shift-down causing acontraction of the oil chamber 63, the resilient place 81 deforms in thedirection opening the communication hole 63, providing little orsubstantially no resistance against the outflow of the oil.

This means that in cases where upon the shift-up a greater gear shiftshock or judder is expected than in the shift-down, use of the inventiveoil damper 80 ensures effectively reduced gear shift shocks or judders.

Referring then to FIG. 8 there is illustrated an embodiment of an oildamper 90 provided with a one-way valve 92.

Similarly to the above embodiments, the same members are designated bythe same reference numerals.

The one-way valve 92 comprises a through-hole 93 formed in a verticalannular wall 91 of the front carrier for allowing the oil chamber 63 tocommunicate with the exterior, a ball 94 fitted externally into agreatly recessed outside opening of the through-hole 93, and a platespring 95 for retaining the ball 94 externally.

In the event of no change in the volume of the oil chamber 63, the ball94 retained by the plate spring 95 blocks the through-hole 93, and uponthe expansion as well the ball 94 is in a sucked state closing thethrough-hole 93, whereas upon the shift-down causing a contraction ofthe volume of the oil chamber 63 a large hydraulic pressure is appliedinternally to the ball 94 to displace the latter against the springforce of the plate spring 95, with the result that the through-hole 93is opened allowing the outflow of oil within the oil chamber 63.

Accordingly, upon the shift-down a less resistance is provided than inthe shift-up, so that in cases where greater gear shift shocks orjudders are expected in the shift-up rather than in the shift-down, useof the inventive oil damper 90 ensures an effective reduction of theshocks or judders induced by gear shifts.

It is also possible to eliminate any influence of a hydraulic pressurewhich may be generated by the centrifugal force within the oil damper90.

Reference is then made to FIG. 9 which illustrates an oil damper 100 inaccordance with another embodiment.

The oil damper 100 has also substantially the same structure as theabove embodiment, in which the same members are designated by the samereference numerals. The inventive oil damper 100 comprises a piston 101of a U-shaped section having an outer tubular portion 102, athrough-hole 103 formed in the outer tubular portion 102 for allowing acommunication between the oil chamber 63 and the exterior, and aresilient plate 104 provided inside of the outer tubular portion 102 forfreely opening and closing the through-hole 103.

In the event of no change in the volume of the oil chamber 63, theresilient plate 104 closes the through-hole 103 under the hydraulicpressure within the oil chamber 63, and upon the contraction as well thethrough-hole 103 is closed by the resilient plate 104 due to the actionof the hydraulic pressure within the oil chamber 63, whereas upon theshift-down causing an expansion of the volume of the oil chamber 63, thehydraulic pressure within the oil chamber 63 is reduced so that theresilient plate 104 deforms as shown in FIG. 9 to open the through-hole103, allowing oil within the oil chamber 63 to flow out.

Accordingly, upon the shift-up a less resistance is provided than in theshift-down, so that in cases where greater gear shift shocks or juddersare expected in the shift-down rather than in the shift-up, use of theinventive oil damper 100 ensures effectively reduced gear shift shocksor judders.

An appropriate weight may fixedly be secured to a site where theresilient plate 104 swings in order to control the timing to open thethrough-hole 103.

It is also possible to eliminate any influence of a hydraulic pressurewhich may be generated by the centrifugal force within the oil damper100.

Reference is then made to FIG. 10 which illustrates an oil damper 120 inaccordance with a further embodiment.

The oil damper 120 has also substantially the same structure as theabove embodiments, in which the same members are designated by the samereference numerals.

It resembles in particular the oil damper 90 shown in FIG. 8, butdiffers therefrom in that a one-way valve of this embodiment has theopposite releasing direction.

More specifically, the one way valve designated at 122 comprises athrough-hole 123 formed in a vertical annular wall 121 of the clutchguide on the front carrier, for allowing a communication between the oilchamber 63 and the exterior, a ball 124 fitted internally into a greatlyrecessed inside opening of the through-hole 123, and a plate 125disposed on the inside and having an opening edge for preventing anypossible disengagement of the ball 122.

Upon the expansion of the oil chamber 63 the peripheral oil is suckedthrough the one-way valve 122, whereas upon the compression thethrough-hole 123 is closed. As a result of this, upon the shift-up aless resistance is provided than in the shift-down, so that in casegreater gear shift shocks or judders are expected upon the shift-down,use of the inventive damper 120 ensures an effective reduction in shocksor judders induced by gear shifts.

INDUSTRIAL APPLICABILITY

The present invention can be applied to a variable speed gearing systemfor reducing gear shift shocks or gear shift judders.

What is claimed is:
 1. A variable speed gearing system including twoclutch units placed side by side in the axial direction, said variablespeed gearing system providing a plurality of transmission gear ratiosin response to the state of engagement of clutches of said two clutchunits, said two clutch units being provided with axially movable membersconfronting each other; said variable speed gearing system comprising: apiston member provided on one of said axially movable membersconfronting each other; and a cylinder member provided on the other ofsaid axially movable members confronting each other, said piston memberand said cylinder member constituting a damper mechanism in combinationwith each other.
 2. The variable speed gearing system according to claim1, further comprising: an oil chamber defined by said piston member andsaid cylinder member in cooperation, said oil chamber having an expandedor contracted volume; and communication passages extending from oilpassages formed within shafts for axially movably supporting saidmovable members of said clutch units, into said oil chamber.
 3. Thevariable speed gearing system according to claim 2, further comprisingflow control means disposed in said communication passages for impartingdifferent passage areas to said communication passages between expansionand contraction of said oil chamber.